IPv4 Subnet & CIDR Calculator
Calculate network address, broadcast address, subnet mask, wildcard mask, and usable host ranges for any IPv4 CIDR prefix.
IPv4 Subnetting & CIDR Address Calculations
Subnetting divides an IP network into smaller sub-networks, enabling efficient allocation of IP addresses across subscriber VLANs, OLT management subnets, and BNG pools.
Proper IPv4 subnetting prevents broadcast storm propagation, optimizes routing table aggregation, and conserves valuable public and private IP space.
Interactive IPv4 Subnet & CIDR Calculator Workspace
Free ISP Engineering & Planning Tools
Precision planning tools for WISPs and fiber operators — RF, optical, power, addressing, and business math. No sign-up required.
Link Budget Calculator
Calculate FSPL, RSSI, and EIRP for wireless links (2.4GHz to 60GHz).
Tower Revenue Calculator
Analyze ISP tower profitability, CAPEX/OPEX, and business Break-Even Point.
GPON Splitter Calculator
Plan optical budgets for PON networks. Calculate splitter and fiber loss.
UPS Runtime Calculator
Estimate battery backup time based on load (Watts) and battery capacity (Ah).
IPv4 Subnet Calculator
CIDR to Subnet Mask, Network Address, Broadcast, and Host Range calculator.
CGNAT Calculator
Plan Carrier-Grade NAT: subscribers per public IPv4, port blocks, and pool capacity.
Data & Bandwidth Converter
Convert Mbps to Gbps, MB to GB, bits to bytes, plus a download time calculator.
Bandwidth Calculator
Plan oversubscription ratios and total backhaul capacity requirements.
ROI Comparison
Compare Kashtrix costs vs legacy platforms (Splynx/Sonar). See how much you can save.
SLA Uptime Calculator
Convert SLA uptime percentages (99.9%) to allowable downtime limits.
MAC Address Lookup
Find the hardware vendor behind any MAC address and decode the OUI bits.
DNS Lookup
Query live A, AAAA, MX, TXT, NS, CNAME and SOA records for any domain.
What Is My IP
See your public IP address, reverse DNS, ISP and location instantly.
IP Location Lookup
Geolocate any IPv4 or IPv6 address: country, city, ISP, ASN and timezone.
CIDR Calculator
Expand a CIDR block to its range, or aggregate an IP range into CIDR blocks.
IPv6 Subnet Calculator
Network, address range, expanded form and subnet counts for any IPv6 prefix.
dBm to Watt Converter
Convert RF power between dBm, mW and watts, and dB gain to a linear ratio.
IPv4 Subnet Calculator
Real-World Calculation Walkthrough
Subnetting 192.168.10.45 with a /24 CIDR prefix
Input Parameters
Calculation Output
IPv4 Subnet & CIDR Calculator Engineering FAQs
Why are 2 IP addresses subtracted from total hosts in a subnet?
The first address represents the Network ID (identifies the subnet) and the last address represents the Broadcast ID (used to send packets to all hosts).
What CIDR prefix is used for point-to-point router links?
Modern networks use /31 (RFC 3021, 2 usable IPs) or /30 (4 total IPs, 2 usable) for point-to-point links between core routers and switches.
How do I calculate wildcard masks for OSPF and ACLs?
A wildcard mask is the bitwise inverse of the subnet mask. For example, a 255.255.255.0 mask yields a wildcard mask of 0.0.0.255.
Explore More Free ISP Engineering Tools
CGNAT Calculator
Calculate CGNAT public IPv4 address requirements, subscriber port block allocations, and NAT444 capacity for ISPs and WISPs.
GPON Splitter & Optical Budget Calculator
Calculate GPON optical power loss, splitter attenuation (1:2 to 1:64), fiber distance loss, and ONT rx signal budget.
IPv6 Subnet & Prefix Calculator
Calculate IPv6 expanded addresses, subnet ranges, prefix breakdowns, and total /64 subnets from any IPv6 prefix (/48, /56, /64).
Wireless Link Budget & FSPL Calculator
Calculate FSPL, RSSI, link margin, and EIRP for outdoor fixed wireless links (2.4GHz, 5GHz, 11GHz, 60GHz, 80GHz).